The present invention relates generally to medical fluid systems and more particularly to the testing and priming of such systems.
It is known in peritoneal dialysis systems to perform integrity tests that attempt to verify that the numerous fluid valves in a disposable cassette do not leak, that leaks do not occur between multiple pump chambers in the cassette, that leaks do not occur across fluid pathways, and that an isolation occluder, which is intended to stop liquid flow in fluid lines connected to the cassette in the event of a system malfunction, is performing that procedure properly. In one known wet leak test described in U.S. Pat. No. 5,350,357, a disposable cassette is loaded into a peritoneal dialysis cycler and the solution bags are connected. The test consists of the following steps:
(i) a negative pressure decay test of the fluid valve diaphragms is performed;
(ii) a positive pressure decay test of the fluid valve diaphragms is performed;
(iii) a positive pressure decay test is performed on the first pump chamber, while a negative pressure decay test is performed on the second pump chamber;
(iv) a negative pressure decay test is performed on the first pump chamber, while a positive pressure decay test is performed on the second pump chamber; after which
(v) both pump chambers are filled with a measured volume of fluid, all fluid valves are opened and the occluder is closed, positive pressure is applied to both pump chambers for a period of time, after which the volume of fluid in each pump chamber is measured again to determine if any fluid has leaked across the occluder.
As indicated, the above testing procedure is performed after solution bags are connected to the peritoneal dialysis system. If integrity of the cassette or tubing is faulty, the sterility of the solution bags becomes compromised. In such a case, both the disposable cassette and solution bags have to be discarded. Additionally, it is possible that liquid from the solution bags can be sucked into the machine's pneumatic system, causing the pneumatic system of the machine to malfunction.
Wet tests are also susceptible to false triggers. In particular, cold solution used in the test causes many false disposable integrity test alarms each year because the tests fail when an occluder, which is supposed to clamp off all fluid lines, does not properly crimp or seal the tubing lines. When the solution is cold, it cools the set tubing to a lower temperature than the tubing would be if placed only in room air. Colder tubing is harder to occlude, allowing fluid in some cases to leak past the occluder and cause the test to fail. Once a dialysis therapy starts, the fluid passing through the tubing is warmed to about 37° C., enabling the occluder to perform satisfactorily.
It is therefore desirable to have an integrity test that is performed before the solution bags are attached to the therapy machine and to eliminate the use of cold solution to prevent false triggers.
A “dry” test is described briefly in U.S. Pat. No. 6,302,653. The description is based in part upon the “dry test”, implemented in the Baxter HomeChoice® cycler in December of 1998. The actual test implemented in the HomeChoice® cycler consists of four steps, the first of which occurs before the solution bags are connected. The next three steps require the solution bags to be connected but do not require fluid to be pulled from the bags into the machine. FIGS. 1 to 4 illustrate the areas of a fluid cassette tested by the individual steps of the known “dry” test. While the above “dry” test eliminates the problem of fluid potentially leaking into the pneumatics of the machine, the test does not prevent the sterility of the bags from being compromised potentially upon a leak and thus from being discarded if the integrity of the disposable cassette is compromised.
Moreover, dry testing with air is believed to be more sensitive than the wet test, which uses dialysis fluid. It is therefore also desirable to have an integrity test that uses air for sensitivity reasons as well as for the reasons stated above.
While integrity testing poses one problem to manufacturers of medical fluid machines, another common problem is the priming of the fluid system within those machines. In many instances, air must be purged from one or more tubes for safety purposes. For example, in the realm of dialysis, it is imperative to purge air from the system, so that the patient's peritoneum or veins and arteries receive dialysis fluid that is free of air. Consequently, automated dialysis machines have been provided heretofore with priming systems. In peritoneal dialysis, the object of priming is to push fluid to the very end of the line, where the patient connector that connects to the patient's transfer set is located, while not priming fluid past the connector, allowing fluid to spill out of the system.
Typically, dialysis machines have used gravity to prime. Known gravity primed systems have a number of drawbacks. First, some priming systems are designed for specifically sized bags. If other sized bags are used, the priming system does not work properly. Second, it happens in many systems that at the beginning of priming, a mixture of air and fluid can be present in the patient line near its proximal end close to a disposable cartridge or cassette. Fluid sometimes collects in the cassette due to the installation and/or integrity testing of same. Such fluid collection can cause air gaps between that fluid and the incoming priming solution. The air gaps can impede and sometimes prevent gravity priming. Indeed, many procedural guides include a step of tapping a portion of the patient line when the line does not appear to be priming properly. That tapping is meant to dislodge any air bubbles that are trapped in the fluid line.
A third problem that occurs relatively often in priming is that the patient forgets to remove the clamp on the patient line prior to priming that line. That clamped line will not allow the line to prime properly. An alarm is needed to inform the patient specifically that the patient needs to remove the clamp from the patient line before proceeding with the remainder of therapy. Fourth, if vented tip protectors are provided at the end of the patient line, the vented tip protectors may not vent properly and impede priming. An alarm is again needed to inform the patient that the line has not primed properly. Fifth, cost is always a factor. Besides providing a priming apparatus and method that overcomes the above problems, it is also desirable to use existing components to perform the priming, if possible, to avoid having to add additional components and additional costs.
Another concern for medical fluid systems and in particular automated peritoneal dialysis (“APD”) systems is ensuring that solution bags are placed at a height relative to the machine that is suitable for the machine to operate within designated parameters. The height of solution bags, such as dialysate bags, lactate bags and/or dextrose bags, needs to be monitored to ensure that the proper amount of fluid will be pumped to the patient during therapy and that the correct amount and proportion of additives are infused. Two patents discussing bag position determination are U.S. Pat. Nos. 6,497,676 and 6,503,062.
The present invention in one primary embodiment performs an integrity test on both the cassette sheeting and the molded cassette features of a disposable cassette. The methodology of the invention is applicable to many cassette based pumping and liquid distribution systems and is particularly suited for dialysis treatment, such as automated peritoneal dialysis. The steps of the integrity test are performed almost exclusively before solution bags, such as peritoneal dialysis solution bags, are connected to a dialysis therapy machine, such as a peritoneal dialysis machine. Such a test is advantageous because if an integrity problem arises, the patient only has to discard the disposable cassette and associated tubing, not the solution. Also, because fluid is not connected to the machine to perform the test, there is no opportunity for fluid, due to a leak, to be sucked into the machine's pneumatics, potentially causing malfunction.
The dry testing of the present invention is performed with all fluid lines capped except for the drain line, which is covered with a tip protector and/or membrane that allows air but not liquid to escape. Because the lines remain capped, they are not connected to the solution bags. Consequently, no solution bags become contaminated if the cassette has a leak.
The testing steps are able to be performed with capped lines for a number of reasons. In some steps, the tip protectors, or caps, connected to all lines except the drain line are left in place because the cassette sheeting and fluid pathways are tested with valves in the open position rather than the closed position. When the valves are open, all of the fluid channels in the cassette are in direct communication with both pump chambers and the drain line, which has a bacteria retentive tip protector that allows air to pass through it. Air from a failed test can therefore pass through the drain line from cassette, changing the pressure in the system so that a leak can be detected.
In other test steps, the tip protectors can be left in place because one part of the system is pressurized, while the other is evacuated. Air leaking from the positively pressurized part of the cassette leaks to the evacuated part and is readily detectable as is air escaping from or leaking into the cassette. Further, because air flows more readily than does water or solution through a leak, the air test is more expedient and sensitive than a fluid based test, increasing accuracy and repeatability and decreasing test time.
The present invention in another primary embodiment provides an apparatus and method for priming a medical fluid delivery system. The priming method and apparatus is described herein for an automated peritoneal dialysis machine, however, the test is applicable to any fluid delivery system, which requires the purging of air for safety or operational reasons. The method and apparatus operates with a system having a fluid container or fluid bag, at least one fluid pump and at least one tubing line, such as a patient line extending from that fluid pump. In a first step of the priming method, valves surrounding the fluid pump are configured so that fluid flows via gravity or via the pump into the pump chamber and fills such pump chamber but does not exit the chamber. In a second step, the valves are switched so that the fluid in the supply bag is no longer able to fill the pump chambers, and so that the pump chambers can be pressurized and thereby pump the fluid from the pump chambers downstream and partially into the patient line. The machine processor is configured to expect a pressure drop in the pump chamber when the pump chamber expels fluid therefrom. If such pressure drop is not seen, the patient has likely forgotten to remove the clamp in the patient line and an error message is generated. In a final step, the valves surrounding the pump are opened so that fluid from the container or bag can continue to flow through and prime the patient line until fluid reaches the end of the patient line, which is positioned at the same elevational height as the top of the fluid in the fluid container.
As indicated above, if the patient line is inadvertently clamped during priming, the pressure in the pump chamber during the pushing step would not fall to an expected level, prompting a suitable alarm. Further, the initial pushing of fluid through the proximal part of the patient line, nearer to the cassette, in many instances will overcome the resistance to fluid flow caused by air trapped in that portion of the line, and allow priming to thereafter take place in a proper manner.
Another primary aspect of the present invention is an apparatus and method for determining the vertical position or head height of one or more solution bags as well as a drain bag. The method and apparatus use atmospheric pressure to establish a zero position relative to the therapy machine, such as an APD machine. The bag height determination can determine whether a solution bag is in the proper position to achieve a desired pumped flowrate, whether the solution bag is properly located on a heater plate, whether the relative position between two or more bags is proper, whether the drain bag is located in a proper position or whether one or more of the bags is empty, etc.
It is therefore an advantage of the present invention to provide an integrity test that consumes less time than previous practices.
It is another advantage of the present invention to provide an integrity test that is more effective at detecting leaks than previous practices.
It is a further advantage of the present invention to provide an integrity test that is more convenient for the patient if a leak is detected.
It is another advantage of the present invention to provide an integrity test that minimizes the supplies that must be discarded if a leak is detected.
It is yet another advantage of the present invention to provide an integrity test that is immune to failure of other machine components, such as a flow line occluder.
It is still another advantage of the present invention to provide an integrity test that does not require warm solution.
It is still a further advantage of the present invention to provide an integrity test from which it is possible for a user to distinguish between a failure of the disposable set and a leak in the pneumatic system of the machine or cycler.
Moreover, it is an advantage of the present invention to eliminate false triggering due to cold solution used in integrity testing.
Still further, it is an advantage of the present invention to provide a priming method and apparatus that operates to automatically dislodge air pockets located initially in the priming line, which would otherwise tend to slow or completely stop priming.
Yet another advantage of the present invention is to provide a priming method and apparatus that detects when the patient or operator has inadvertently left a clamp on the priming line, so that the therapy machine can generate a suitable alarm.
Further still, an advantage of the present invention is to be able to determine the elevational location and head height of one or more solution and drain bags.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures.